Distributing Root CA Certificate to Domain

At this time, distribute the root CA certificate to the domain by importing the root CA certificate into Trusted Root CA of Public Key Policies at an intended domain level GPO, and then the subordinate CA is in place.
Open Group Policy Management, then right-click Default Domain Policy, and then click Edit.

In the Computer Configuration node, expand Policies, expand Windows Settings, expand Security Settings, expand Public Key Policies, right-click Trusted Root Certification Authorities, and then click Import...